<meta charset="utf-8">
<title>Hidden e outros elementos de formulários</title>

<?php
	if (isset($_POST['envia'])) {
		$f['teste'] = $_POST['teste'];
		$f['data'] = $_POST['oculto'];

		echo "<pre>";
			print_r($f);
		echo "</pre>";
	}else;

?>

<form name="formTest" action="" method="post">
	<label>
		<input type="text" name="teste" value="">
	</label>

	<input type="hidden" name="oculto" value="<?php echo date('Y'); ?>">
	<input type="submit" name="envia" value="Enviar">
</form>